The transforming gene of avian acute leukemia virus E26 contains two distinct oncogenes, v-mybE and v-ets, joined in tandem as a result of recombination with two different proto-oncogenes, c-myb and c-ets. In vivo, E26 induces erythroblastosis and myeloblastosis, presumably due to the action of v-ets and v-mybE, respectively. In contrast, the c-ets proto-oncogene is primarily expressed in lymphoid tissues. The differential expression of v-ets and c-ets in hematopoietic cells raises the possibility that the normal function of c-ets has been subverted by retroviral recombination to redirect its growth promoting potential to new hematopoietic target cells. The specific aims of this proposal are (1) to determine whether v-mybE and v-ets exert their functions on avian hematopoietic cells independently or whether the action of one v-onc gene affects the activity of the other, and (2) to determine the functions of c-ets, its relation to v-ets and its latent leukemogenic potential. The transforming gene of E26, v-mybE-ets, will be inserted into a replication competent vector and transfected into chick embryo fibroblasts. The virus generated from the transfected cells will be tested for its ability to transform hematopoietic cells in culture and for leukemogenesis in chickens. Mutations will be created in either the v-mybE or v-ets gene in order to determine whether modification of one v-onc gene will affect the oncogenic potential of the other. A c-ets cDNA will be cloned from a library derived from chicken spleen messenger RNA and the relationship of c-ets and v-ets will be delineated by nucleotide sequence comparisons. The latent leukemogenic functions of c-ets will be tested by inserting c-ets cDNA itself or chimeric constructs of v-ets/c-ets and v-mybE/c-ets into the retrovirus vector and testing their transforming potential in vitro and in vivo. Human c-ets has been mapped to two different loci on chromosomes 11 and 21. The c-ets-1 locus on chromosome 11q23-24 is a frequent breakpoint in chromosome translocations observed in human acute lymphoblastic leukemia (ALL). Thus, the c-ets gene and its product will be studied in cases of human ALL to see if there are characteristic structural alterations of c-ets in human leukemia.